The objective of this research is to evaluate the hypothesis that C3 variants are related to the development of mesangiocapillary glomerulonephritis (MCGN). We have preliminary data in two families that an autosomally inherited co-dominant "hypomorphic variant (C3f)" is associated with hypocomplementemic forms of glomerulonephritis. Previous workers have not studied C3 typing in glomerulonephritis and the single family previously reported with C3f was normal. By collaborative arrangements with area nephrologists, sera will be obtained from patients with MCGN and other forms of glomerulonephritis. C component titrations will be correlated with morphology (light immunofluorescent and electron microscopy) and Complement (C) titrations include protein and hemolytic methods. C3 typing is by prolonged agarose electrophoresis followed by spectrodensitometry of dried and stained plates. C3 Nephritic Factor is titered by a Mg ions dependent hemolytic assay. Normal sera and sera from patients with other forms of glomerulonephritis besides MCGN will be studied. These data will permit evaluation of current subtypes of MCGN (Type I, Type II) as well as evaluation of the possibility that genetically determined C3 variants may be related to acquisition of MCGN and other forms of glomerulonephritis.